McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 251. |
The actual temperature drop across the heating surface of an evaporator depends on the |
| A. | Liquid depth over the heating surface |
| B. | Solution being evaporated |
| C. | Pressure difference between the steam chest and the vapor space above the boiling liquid |
| D. | All (A), (B) and (C) |
| Answer» D. All (A), (B) and (C) | |
| 252. |
In SI units, thermal conductivity is expressed in |
| A. | Watt/m.°K |
| B. | Watt/m2. °K |
| C. | Watt/m2. °K |
| D. | Watt/m4. °K |
| Answer» A. Watt/m.°K | |
| 253. |
jH factor for heat transfer depends upon the __________ number. |
| A. | Biot |
| B. | Nusselt |
| C. | Reynolds |
| D. | Prandtl |
| Answer» C. Reynolds | |
| 254. |
In pipe flow, heat is transferred from hot wall to the liquid by |
| A. | Conduction only |
| B. | Forced convection only |
| C. | Forced convection and conduction |
| D. | Free and forced convection |
| Answer» C. Forced convection and conduction | |
| 255. |
A perfect black body is a perfect __________ of radiation. |
| A. | Absorber |
| B. | Emitter |
| C. | Both (A) & (B) |
| D. | Neither (A) nor (B) |
| Answer» C. Both (A) & (B) | |
| 256. |
Heat transfer rate described by Fourier's law will decrease, if the __________ increases. |
| A. | Thermal conductivity |
| B. | Thickness |
| C. | Temperature difference |
| D. | Heat transfer area |
| Answer» B. Thickness | |
| 257. |
The absorptivity of a body is equal to its emissivity |
| A. | At a particular temperature |
| B. | For circular bodies |
| C. | Under thermal equilibrium |
| D. | None of these |
| Answer» C. Under thermal equilibrium | |
| 258. |
In a co-current double pipe heat exchanger used for condensing saturated steam over the inner tube, if the entrance and exit conditions of the coolant are interchanged, then the rate of condensation will |
| A. | Increase |
| B. | Decrease |
| C. | Remain unchanged |
| D. | Either increase or decrease; depends on the coolant flow rate |
| Answer» C. Remain unchanged | |
| 259. |
The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m-2 .°C-1 . The rate of heat loss from the outer surface in W.m-2 is |
| A. | 165.4 |
| B. | 167.5 |
| C. | 172.5 |
| D. | 175 |
| Answer» A. 165.4 | |
| 260. |
Which one gives the monochromatic emissive power for black body radiation? |
| A. | Planck's law |
| B. | Kirchhoff’s law |
| C. | Wien's law |
| D. | Stefan-Boltzmann law |
| Answer» A. Planck's law | |
| 261. |
If heat transfer rate varies with the time, it is termed as |
| A. | Forced convection |
| B. | Steady state conduction |
| C. | Monochromatic radiation |
| D. | None of these |
| Answer» D. None of these | |
| 262. |
Absorptivity and reflectivity of a perfect black body are respectively |
| A. | 1 and 0 |
| B. | 0 and 1 |
| C. | 1 and ∞ |
| D. | 0 and 0.5 |
| Answer» A. 1 and 0 | |
| 263. |
__________ heat exchanger is used for chilling oil to be dewaxed. |
| A. | U-tube |
| B. | Double pipe |
| C. | Fixed tube |
| D. | Floating head |
| Answer» B. Double pipe | |
| 264. |
Pick out the correct equation. |
| A. | jH = (St)(Pr) 2/3 = f/2 |
| B. | jH = (St)(Pr) 1/3 = f/2 |
| C. | jH = (St) 2/3(Pr) = f/2 |
| D. | jH = (St) 1/3(Pr) = f/2 |
| Answer» A. jH = (St)(Pr) 2/3 = f/2 | |
| 265. |
It is not preferable to use superheated steam in evaporators, because of its very |
| A. | High temperature |
| B. | High pressure |
| C. | Low film co-efficient |
| D. | None of these |
| Answer» C. Low film co-efficient | |
| 266. |
Water is normally used as a coolant in the heat exchange equipments mainly because of its |
| A. | Abundance & high heat capacity |
| B. | Low density |
| C. | Low viscosity |
| D. | High fluidity |
| Answer» A. Abundance & high heat capacity | |
| 267. |
A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of |
| A. | 2 |
| B. | 2 0.8 |
| C. | 2 0.2 |
| D. | 2 0.5 |
| Answer» B. 2 0.8 | |
| 268. |
At constant temperature, the thermal conductivities of gases __________ with rise in pressure. |
| A. | Decrease |
| B. | Increase |
| C. | Remain unchanged |
| D. | May increase or decrease; depends on the pressure |
| Answer» A. Decrease | |
| 269. |
Stefan-Boltzmann law applies to __________ body. |
| A. | Black |
| B. | White |
| C. | Grey |
| D. | Any colour |
| Answer» A. Black | |
| 270. |
When warm and cold liquids are mixed, the heat transfer is mainly by |
| A. | Conduction |
| B. | Convection |
| C. | Radiation |
| D. | Both (A) & (C) |
| Answer» B. Convection | |
| 271. |
A BTU/hr.ft.2 °F is equal to |
| A. | 1 kcal/hr. m2 °C |
| B. | 4.88 kcal/hr. m.2 °C |
| C. | 1 kcal/hr. m2 .°K |
| D. | None of these |
| Answer» B. 4.88 kcal/hr. m.2 °C | |
| 272. |
Open pan evaporators are preferred to be used, when the solution to be concentrated is |
| A. | Scaling |
| B. | Highly viscous |
| C. | Corrosive |
| D. | Salty |
| Answer» B. Highly viscous | |
| 273. |
A __________ evaporator employs an annular downtake. |
| A. | Basket type |
| B. | Horizontal |
| C. | Long tube vertical |
| D. | None of these |
| Answer» A. Basket type | |
| 274. |
The equation, Nst = (f/2)/[1 + 5 (Npr - 1) √(f/2)], corresponds to __________ analogy. |
| A. | Von-Karman |
| B. | Reynolds |
| C. | Colburn |
| D. | Prandtl |
| Answer» D. Prandtl | |
| 275. |
The advantage of using a 1 - 2 shell and tube heat exchanger over a 1 - 1 shell and tube heat exchanger is |
| A. | Lower tube side pressure drop |
| B. | Lower shell side pressure drop |
| C. | Higher tube side heat transfer co-efficient |
| D. | Higher shell side heat transfer co-efficient |
| Answer» C. Higher tube side heat transfer co-efficient | |
| 276. |
With increase in temperature, the thermal conductivity of fresh lubricating oil |
| A. | Increases |
| B. | Decreases |
| C. | Remains unchanged |
| D. | May increase or decrease; depends on its composition |
| Answer» B. Decreases | |
| 277. |
Vent pipes are provided in a condenser to |
| A. | Remove non-condensable gases |
| B. | Purge the condenser |
| C. | Facilitate easy cleaning of tubes |
| D. | None of these |
| Answer» A. Remove non-condensable gases | |
| 278. |
To reduce the tube side pressure drop for the same flow rate, the heat exchanger recommended is |
| A. | 1-2 heat exchanger |
| B. | 1-1 heat exchanger |
| C. | 3-2 heat exchanger |
| D. | 2-4 heat exchanger |
| Answer» B. 1-1 heat exchanger | |
| 279. |
LMTD for counter-flow and parallel flow heat exchanger will be the same, when the |
| A. | Cold fluid is heated to a certain temperature by condensing steam (isothermal fluid) |
| B. | Outlet temperature of both the hot and cold fluid are same |
| C. | Outlet temperature of hot fluid is less than the outlet temperature of the cold fluid |
| D. | None of these |
| Answer» A. Cold fluid is heated to a certain temperature by condensing steam (isothermal fluid) | |
| 280. |
In case of __________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface. |
| A. | Nucleate |
| B. | Local |
| C. | Pool |
| D. | Saturated |
| Answer» B. Local | |
| 281. |
Steam trap is used to |
| A. | Condense the steam flowing in the pipeline |
| B. | Remove water resulting from partial condensation of steam |
| C. | Stop the supply of steam |
| D. | None of these |
| Answer» B. Remove water resulting from partial condensation of steam | |
| 282. |
For __________ Prandtl number values, the heat conduction will be negligible in the buffer zone. |
| A. | Extremely low |
| B. | Low |
| C. | High |
| D. | No |
| Answer» C. High | |
| 283. |
Planck's distribution law is valid for __________ bodies. |
| A. | Black |
| B. | White |
| C. | Coloured |
| D. | All (A), (B) & (C) |
| Answer» C. Coloured | |
| 284. |
Electro-magnetic spectrum range, which is important for radiation varies from __________ microns. |
| A. | 1 to 100 |
| B. | 0.5 to 50 |
| C. | 10 to 100 |
| D. | 100 to 1000 |
| Answer» B. 0.5 to 50 | |
| 285. |
In a shell and tube heat exchanger, square pitch compared to triangular pitch |
| A. | Gives a higher shell side pressure drop |
| B. | Gives a lower shell side pressure drop |
| C. | Can pack more surface area into a shell of given diameter |
| D. | None of these |
| Answer» A. Gives a higher shell side pressure drop | |
| 286. |
A body cools down from 75°C to 70°C in 10 minutes. It will cool down from 70° C to 65° C in __________ minutes. |
| A. | 10 |
| B. | > 10 |
| C. | < 10 |
| D. | Either (B) or (C), depends on the mass of the body |
| Answer» B. > 10 | |
| 287. |
In a gas-liquid shell and tube heat exchanger, the |
| A. | Presence of a non-condensable gas decreases the condensing film co-efficient |
| B. | Gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature |
| C. | Gases to be heated/cooled is normally routed through the shell side, because the corrosion caused by the cooling water or steam condensate remain localised to the tubes |
| D. | All 'a', 'b' & 'c' |
| Answer» D. All 'a', 'b' & 'c' | |
| 288. |
For large heat transfer area requirement, shell and tube heat exchanger is preferred, because it |
| A. | Occupies smaller space |
| B. | Is more economical |
| C. | Is easy to operate and maintain |
| D. | All (A), (B) and (C) |
| Answer» D. All (A), (B) and (C) | |
| 289. |
Terminal point temperature differences between fluids in case of a heat exchanger is termed as |
| A. | Approach |
| B. | Log mean temperature difference |
| C. | Arithmetic mean temperature difference |
| D. | Geometric mean temperature difference |
| Answer» A. Approach | |
| 290. |
The Stefan-Boltzmann constant depends on the |
| A. | Medium |
| B. | Temperature |
| C. | Surface |
| D. | None of these |
| Answer» D. None of these | |
| 291. |
A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when |
| A. | CPA > CPB |
| B. | CPA < CPB |
| C. | kA < 0.5 kB |
| D. | kA >2 kB |
| Answer» C. kA < 0.5 kB | |
| 292. |
In a shell and tube type heat exchanger, the floating tube bundle heat arrangement is used |
| A. | In low range of temperature differences |
| B. | In high range of temperature differences |
| C. | Because of its low cost |
| D. | To prevent corrosion of the tube bundles |
| Answer» B. In high range of temperature differences | |
| 293. |
Overall heat transfer co-efficient of a particular tube is U1. If the same tube with some dirt deposited on either side has coefficient U2, then |
| A. | U1 = U2 |
| B. | U2 > U1 |
| C. | U1 > U2 |
| D. | U1 = dirt factor - U2 |
| Answer» A. U1 = U2 | |
| 294. |
In forced convection, the Nusselt number is a function of |
| A. | Re and Pr |
| B. | Re and Gr |
| C. | Pr and Gr |
| D. | Re and Sc |
| Answer» A. Re and Pr | |
| 295. |
Maximum heat transfer rate is achieved in __________ flow. |
| A. | Co-current |
| B. | Counter-current |
| C. | Turbulent |
| D. | Laminar |
| Answer» C. Turbulent | |
| 296. |
Radiator of an automobile engine is a __________ type of heat exchanger. |
| A. | Co-current |
| B. | Cross-current |
| C. | Counter-current |
| D. | Direct contact |
| Answer» D. Direct contact | |
| 297. |
Temperature profile in steady state heat transfer is |
| A. | Asymptotic |
| B. | Hyperbolic |
| C. | Parabolic |
| D. | Linear |
| Answer» D. Linear | |
| 298. |
Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger? |
| A. | Tube side pressure drop and the heat transfer rate |
| B. | Convective heat transfer co-efficient |
| C. | Effective tube surface area for convective heat transfer |
| D. | All (A) (B) and (C) |
| Answer» D. All (A) (B) and (C) | |
| 299. |
A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is __________ °C. |
| A. | 6 |
| B. | 12 |
| C. | 18 |
| D. | 24 |
| Answer» B. 12 | |
| 300. |
Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is |
| A. | 0.5 |
| B. | 2 |
| C. | 10 |
| D. | 100 |
| Answer» B. 2 | |
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